Nervous tissue

Nervous tissue

 is one of four major classes of vertebrate tissue. It is the specialized tissue that makes up the central nervous system and the peripheral nervous system, consisting of neuronswith their processes, other specialized or supporting cells, and extracellular material.

Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions. It is composed of neurons, which transmit impulses, and the neuroglia cells, which assist propagation of the nerve impulse as well as provide nutrients to the neuron.

Nervous tissue is made of nerve cells that come in many varieties, all of which are distinctly characteristic by the axon or long stem like part of the cell that sends action potential signals to the next cell.

Functions of the nervous system are sensory input, integration, controls of muscles and glands, homeostasis, and mental activity.

All living cells have the ability to react to stimuli. Nervous tissue is specialized to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. Nerve tissue (as in the brain, spinal cord and peripheral nerves that branch throughout the body) are all made up of specialized nerve cells called neurons. Neurons are easily stimulated and transmit impulses very rapidly. A nerve is made up of many nerve cell fibers (neurons) bound together by connective tissue. A sheath of dense connective tissue, the epineurium surrounds the nerve. This sheath penetrates the nerve to form the perineurium which surrounds bundles of nerve fibers. Blood vessels of various sizes can be seen in the epineurium. Theendoneurium, which consists of a thin layer of loose connective tissue, surrounds the individual nerve fibers.

The cell body is enclosed by a cell (plasma) membrane and has a central nucleus. Granules called Nissl bodies are found in the cytoplasm of the cell body. Within the cell body, extremely fine neurofibrils extend from the dendrites into the axon. The axon is surrounded by the myelin sheath, which forms a whitish, non-cellular, fatty layer around the axon. Outside the myelin sheath is a cellular layer called the neurilemma or sheath of Schwann cells. The myelin sheath together with the neurilemma is also known as the medullary sheath. This medullary sheath is interrupted at intervals by the nodes of Ranvier.

Disorders of the Nervous System

Term	Definition	Cause	Effect
Bell's Palsy	A form of Neuritis that involves paralysis of the facial nerve causing weakness of the muscles of one side of the face and an inability to close the eye.	Unknown. (Recovery may occur spontaneously.)	Paralysis of the facial nerve; weakness of the muscles of one side of the face; may result in inability to close the eye. (In some cases the patient's hearing may also be affected in such a way that sounds seem to him/her to be abnormally loud. Loss of taste sensation may also occur.)
Cerebal Palsy	A nonprogressive disorder of movement resulting from damage to the brain before, during, or immediately after birth.	Cerebal Palsy is attributed to damage to the brain, generally occuring before, during, or immediately after birth. It is often associated with other neurological and mental problems.There are many causes including birth injury, hypoxia, hypoglycaemia, jaundice and infection.	The most common disability is a spastic paralysis. Sensation is often affected, leading to a lack of balance, and intelligence, posture and speech are frequently impaired. Contractures of the limbs may cause fixed abnormalities. Other associated features include epilepsy, visual impairment, squint, reduced hearing, and behavioural problems.
Motor Neurone Disease	A progressive degenerative disease of the motor system occurring in middle age and causing muscle weakness and wasting.	Some forms of Motor Neurone Disease are inherited.	Motor Neurone disease primarily affects the cells of the anterior horn of the spinal cord, the motor nuclei in the brainstem, and the corticospinal fibres.
Multiple Sclerosis	A chronic disease of the nervous system that can affect young and middle-aged adults. The course of this illness usually involves recurrent relapses followed by remissions, but some patients experience a chronic progressive course.	The myelin sheaths surrounding nerves in the brain and spinal cord are damaged, which affects the function of the nerves involved. The underlying cause of the nerve damage remains unknown.	Multiple Scerosis affects different parts of the brain and spinal cord, resulting in typically scattered symptoms. These can include: Unsteady gait and shaky movement of the limbs (ataxia); Rapid involuntary movements of the eyes (nystagmus); Defects in speech pronunciation (dysarthria); Spastic weakness and retrobulbar neuritis (= inflammation of the optic nerve).
Myalgic Encephalomyelitis (ME)	A condition characterized by extreme disabling fatigue that has lasted for at least six months, is made worse by physical or mental exertion, does not resolve with bed rest, and cannot be attributed to other disorders.	Unknown. Often occurs as a sequel to such viral infections as glandular fever.	Extreme disabling fatigue that has lasted for at least six months, is made worse by physical or mental exertion, does not resolve with bed rest, and cannot be attributed to other disorders. The fatigue is accompanied by at least some of the following: Muscle pain or weakness; Poor co-ordination; Joint pain; Sore throat; Slight fever; Painful lymph nodes in the neck and armpits; Depression; Inability to concentrate; General malaise.
Neuralgia		Maybe due to previous attack of shingles (Postherpetic Neuralgia).	A severe burning or stabbing pain often following the course of a nerve.
Neuritis	A disease of the peripheral nerves showing the pathological changes of inflammation. (This term may also be less precisely used to refer to anydisease of the peripheral nerves, usually causing weakness and numbness.)		Inflammation of the nerves, which may be painful.
Parkinson's Disease	Degenerative disease process (associated with aging) that affects the basal ganglia of the brain.	Associated with a deficiency of the neurotransmitter dopamine. Also associated with aging.	Tremor, rigidity and poverty of spontaneous movements. The commonest symptom is tremor, which often affects one hand, spreading first to the leg on the same side then to the other limbs. It is most profound in resting limbs, interfering with such actions as holding a cup. The patient has an expressionless face, an unmodulated voice, an increasing tendency to stoop, and a shuffling walk.
Sciatica	A common condition arising from compression of, or damage to, a nerve or nerve root.	Usually caused by degeneration of an intervertebral disc, which protrudes laterally to compress a lower lumbar or an upper sacral spinal nerve root.The onset may be sudden, brought on by an awkward lifting or twisting movement.	Pain felt down the back and outer side of the thigh, leg, and foot. The back is stiff and painful. There may be numbness and weakness in the leg.

Guillain-Barre syndrome 

is a rare disorder that causes your immune system to attack your peripheral nervous system (PNS). The PNS nerves connect your brain and spinal cord with the rest of your body. Damage to these nerves makes it hard for them to transmit signals. As a result, your muscles have trouble responding to your brain. No one knows what causes the syndrome. Sometimes it is triggered by an infection, surgery or a vaccination.

The first symptom is usually weakness or a tingling feeling in your legs. The feeling can spread to your upper body. In severe cases, you become almost paralyzed. This is life-threatening. You might need a respirator to breathe. Symptoms usually worsen over a period of weeks, then stabilize. Most people recover. Recovery can take a few weeks to a few years. Treatment options during the symptom period include medicines or a procedure called plasma exchange.

Multiple sclerosis (MS) is a nervous system disease that affects your brain and spinal cord. It damages the myelin sheath, the material that surrounds and protects your nerve cells. This damage slows down or blocks messages between your brain and your body, leading to the symptoms of MS. They can include

• Visual disturbances
• Muscle weakness
• Trouble with coordination and balance
• Sensations such as numbness, prickling, or "pins and needles"
• Thinking and memory problems

No one knows what causes MS. It may be an autoimmune disease, which happens when your body attacks itself. Multiple sclerosis affects women more than men. It often begins between the ages of 20 and 40. Usually, the disease is mild, but some people lose the ability to write, speak or walk. There is no cure for MS, but medicines may slow it down and help control symptoms. Physical and occupational therapy may also help.

Multiple sclerosis

(MS) is a nervous system disease that affects your brain and spinal cord. It damages the myelin sheath, the material that surrounds and protects your nerve cells. This damage slows down or blocks messages between your brain and your body, leading to the symptoms of MS. They can include

• Visual disturbances
• Muscle weakness
• Trouble with coordination and balance
• Sensations such as numbness, prickling, or "pins and needles"
• Thinking and memory problems

No one knows what causes MS. It may be an autoimmune disease, which happens when your body attacks itself. Multiple sclerosis affects women more than men. It often begins between the ages of 20 and 40. Usually, the disease is mild, but some people lose the ability to write, speak or walk. There is no cure for MS, but medicines may slow it down and help control symptoms. Physical and occupational therapy may also help.

Glioma 

is a type of tumor that starts in the brain or spine. It is called a glioma because it arises from glial cells. The most common site of gliomas is the brain

A stroke 

happens when blood flow to a part of the brain stops. A stroke is sometimes called a "brain attack.

If blood flow is stopped for longer than a few seconds, the brain cannot get blood and oxygen. Brain cells can die, causing permanent damage.

There are two major types of stroke: ischemic stroke and hemorrhagic stroke.

Ischemic stroke occurs when a blood vessel that supplies blood to the brain is blocked by a blood clot. This may happen in two ways:

• A clot may form in an artery that is already very narrow. This is called a thrombotic stroke.
• A clot may break off from another place in the blood vessels of the brain, or from some other part of the body, and travel up to the brain. This is called cerebral embolism, or an embolic stroke.

Ischemic strokes may be caused by clogged arteries. Fat, cholesterol, and other substances collect on the artery walls, forming a sticky substance called plaque.

Trembling fingers